Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention refers to a workpiece machining process and a numerically controlled lathe, particularly for performing said process.
2. Description of the Related Art
In conventional processes for machining workpieces of substantially annular or short tubular shape, such as races for rolling contact bearings, blanks are fed one by one to a lathe to be turned to a desired shape. The blanks are either forged or, in some instances, pieces cut in small lengths from a tube.
The cutting of the tubes requires an expenditure of time and costs concerning the tube cutting machines, resulting in an increase of manufacturing cost. Another inconvenience encountered with the cutting of tubes in small lengths prior to their feeding to the lathe concerns waste, as at least 3 to 5% scrap is left from the tube cutting operations.
In the industry there is an ever increasing demand for numerically controlled automatic lathes adapted to machine low, medium and high volume production. As known, low volume production requires frequent resetting of the automatic machine in passing from one kind of workpiece to another, whilst high volume production machines are generally scarcely flexible as being specifically designed for a certain product.
Against the foregoing background, it is an object of the present invention to provide a numerically controlled lathe capable of machining indifferently forged blanks or tubes to be cut in a plurality of pieces, thereby avoiding the above discussed prior art inconveniences.
It is an object of the present invention to provide a numerically controlled lathe being flexible to deal with low, medium or high volume production, and easy to reset in passing from one kind of workpiece to another.
To meet these and other objects, the invention provides, according to a first aspect, a numerically controlled lathe including a single drum having at least two spindles, the drum being rotatably mounted about a drum axis for selectively moving said spindles between at least a first operational spindle location and a second operational spindle location. The lathe includes at least one toolholder turret with at least one turning tool positionable in working relation to a workpiece retained at one of said spindles at one of said first and second spindle locations. The lathe also includes a workpiece feeding station at one side of the lathe, equipped with a first mechanism for feeding elongate blanks in form of tubes or bars and a second mechanism for feeding pre-formed blanks to a loading location. The lathe further includes an automatic workpiece handling device with a workpiece gripping mechanism pivotable about an axis perpendicular to said drum axis. The lathe additionally includes an automatic transfer apparatus equipped with at least two spaced apart workpiece clamping mechanisms, said apparatus having a first range of motion such that said clamping mechanisms are adapted to be moved parallel to said drum axis and a second range of motion such that the clamping mechanisms are adapted to be moved between said first operational spindle location, said loading location, and said automatic workpiece handling device. The lathe includes a tube cutting mechanism having a range of motion including an active position for engaging and cutting off an end portion of an elongate blank retained at one of said spindles. The lathe also includes an unloading mechanism for delivering a machined workpiece from one of said clamping means to outfeed a receiving mechanism.
According to another aspect of the invention, there is provided a workpiece machining process for producing a plurality of annular or tubular elements from an elongate tubular blank, including the steps of:
(a) providing at least one elongate tubular blank having a length calculated as a function of the number and length of the elements to be obtained therefrom;
(b) feeding said at least one tubular blank at a feeding station of a numerically controlled lathe having a single rotatable drum with at least two spindles;
(c) automatically transferring one said tubular blank from the feeding station and inserting said tubular blank in an axially elongate seat provided at a first spindle of the lathe;
(d) releasably securing said tubular blank in said seat leaving at least part of one surface of the tubular blank accessible to at least one turning tool of the lathe;
(e) automatically moving either of said first spindle and said turning tool relative to one another so as to bring said accessible tubular blank surface within reach of said turning tool;
(f) turning at least part of said accessible surface of the tubular blank;
(g) automatically extracting said tubular blank out of said seat by a length calculated as function of a length of an element to be obtained, leaving an outer portion of the tubular blank protruding from said seat, and automatically moving either of said first spindle and a tube cutting tool relative to one another so as to bring said tubular blank within reach of the cutting tool;
(h) automatically cutting said protruding portion off the tubular with the tube cutting tool, thereby obtaining the annular or tubular element;
(i) automatically removing said annular or tubular element from the first spindle;
(j) pivoting said annular or tubular element 180 degrees about an axis perpendicular to its longitudinal axis to a pivoted position and transferring the element to a second spindle of the lathe;
(k) releasably securing the element in said pivoted position to the second spindle leaving at least part of a surface of the element accessible to at least one turning tool of the lathe;
(l) turning at least part of said accessible surface of the element;
(m) automatically removing the element from the second spindle and delivering the element to an outfeed mechanism; and
(n) cyclically repeating steps (e) to (m) until the last of the elements obtained from the tubular blank is finished.
In order that the present invention may be well understood, there will now be described a preferred embodiment thereof, given by way of example, reference being made to the accompanying drawings, in which: